Commitments and Contingencies - Aircraft Contractual Purchase Commitments (Details)	Sep. 30, 2015 aircraft
Long-term Purchase Commitment [Line Items]
Future Aircraft To Be Received, Remainder of FIscal Year	4
Future Aircraft To Be Received, in Two Years	16
Future Aircraft To Be Received, in Three Years	18
Future Aircraft To Be Received, in Four Years	13
Future Aircraft To Be Received, in Five Years	13
Future Aircraft To Be Received, in Six Years	13
Future Aircraft To Be Received, in Seven Years	18
Future Aircraft To Be Received	95
Airbus [Member] | A320 [Member]
Long-term Purchase Commitment [Line Items]
Future Aircraft To Be Received, Remainder of FIscal Year
Future Aircraft To Be Received, in Two Years	3
Future Aircraft To Be Received, in Three Years	8
Future Aircraft To Be Received, in Four Years	2
Future Aircraft To Be Received, in Five Years
Future Aircraft To Be Received, in Six Years
Future Aircraft To Be Received, in Seven Years
Future Aircraft To Be Received	13
Airbus [Member] | A320 NEO [Member]
Long-term Purchase Commitment [Line Items]
Future Aircraft To Be Received, Remainder of FIscal Year
Future Aircraft To Be Received, in Two Years
Future Aircraft To Be Received, in Three Years
Future Aircraft To Be Received, in Four Years	6
Future Aircraft To Be Received, in Five Years	3
Future Aircraft To Be Received, in Six Years	13
Future Aircraft To Be Received, in Seven Years	18
Future Aircraft To Be Received	40
Airbus [Member] | A321 [Member]
Long-term Purchase Commitment [Line Items]
Future Aircraft To Be Received, Remainder of FIscal Year	3
Future Aircraft To Be Received, in Two Years	9
Future Aircraft To Be Received, in Three Years	10
Future Aircraft To Be Received, in Four Years	5
Future Aircraft To Be Received, in Five Years
Future Aircraft To Be Received, in Six Years
Future Aircraft To Be Received, in Seven Years
Future Aircraft To Be Received	27
Airbus [Member] | A321 NEO [Member]
Long-term Purchase Commitment [Line Items]
Future Aircraft To Be Received, Remainder of FIscal Year
Future Aircraft To Be Received, in Two Years
Future Aircraft To Be Received, in Three Years
Future Aircraft To Be Received, in Four Years
Future Aircraft To Be Received, in Five Years	10
Future Aircraft To Be Received, in Six Years
Future Aircraft To Be Received, in Seven Years
Future Aircraft To Be Received	10
Third Party Lessor [Member] | A320 NEO [Member]
Long-term Purchase Commitment [Line Items]
Future Aircraft To Be Received, Remainder of FIscal Year	1
Future Aircraft To Be Received, in Two Years	4
Future Aircraft To Be Received, in Three Years
Future Aircraft To Be Received, in Four Years
Future Aircraft To Be Received, in Five Years
Future Aircraft To Be Received, in Six Years
Future Aircraft To Be Received, in Seven Years
Future Aircraft To Be Received	5